A Nanofabricator.

A Nanofabricator (or nanofab) is a mainframe device which can be accessed to buy and sell items, including weapons and augments. Once a Nanofabricator has been hacked, it can be accessed by an agent on any adjacent tile. Each Nanofabricator has a random selection of items for sale.

There are two types of Nanofabricator: a basic Nanofabricator with a limited selection of items can be found in every facility, and an unlocked Nanofabricator with a wider selection of items is found in each Nanofab Vestibule mission. The items, weapons and augments available from a Nanofabricator can be bought for their nominal value in credits; Monst3r's Fabricator Multithreading augment gives him a 15% discount if he is the agent making the purchase.

In addition to the items available to buy from a Nanofabricator, it is also possible to sell items from the agent's inventory. All items, except for augments which are already installed, and some special items, can be sold for half of their nominal value, rounded up to the nearest credit. If an item has been sold at a Nanofabricator, it can still be bought back at the same price it was sold for.

Some items are only available from a Nanofabricator before or after certain “days” in in-game time. Some lower-tier items only available on days 1 and 2, and some higher-tier items and more powerful weapons are only available from day 2 onwards. Otherwise, the same items, weapons and augments are potentially available from all Nanofabricators.

Nanofabricators provide soft cover, allowing agents to hide on adjacent tiles.

Most nanofabs have advanced security protocols to prevent unlicensed fabrications.
—Central

The basic type of Nanofabricator is found in every facility, even in special missions, except for the Tutorial mission. The selection of items available to purchase includes one random augment, one random weapon, a Med Gel, a Charge Pack, and two other random items. The two other random items may sometimes be two of the same type of item.

The basic Nanofabricator is always found in an “alcove” 3 tiles wide.

Not all nanofabs are created equal. You've found a good one, there.
—Central

A unlocked Nanofabricator is found in the objective room of a Nanofab Vestibule mission, in addition to the basic Nanofabricator found elsewhere in the facility. The selection of items available to purchase includes 4 random augments, 4 random weapons, a Med Gel, a Charge Pack, and 6 other random items. The selection may include multiples of the same types of item, weapon or augment.

The same items, weapons and augments are potentially available as from a basic Nanofabricator, and the cost of the items is the same; the only benefit of buying from an unlocked Nanofabricator is having more to choose from.